The approach to take Aer Lingus private by chief executive Mr Willie Walsh is seen as a "highly opportunistic" bid for the company, according to informed political sources.

They said the surprise manoeuvre by Mr Walsh will put the Government into a position in which it will have to bring forward the ultimate decision on the future of the airline.

The Government is empowered to sell its shares in the State airline, but it has not yet appointed financial advisers to manage that process.

As the Departments of Transport and Finance move to take independent legal advice on the approach and consult with the Attorney General, there was a recognition last night that Mr Walsh's move will force the Government's hand one way or the other.

In the absence of any firm information from Mr Walsh and because he has expressed only a tentative interest in a buy-out, there was still uncertainty about the extent of the work he has carried out on the proposal.

It is understood that the Department of Transport has told Mr Walsh not to proceed any further in the process until the Government decides its stance. It has also told him that he should not assume that the Minister for Transport, Mr Brennan, will support the initiative.

SIPTU is seeking a meeting with Mr Brennan to express its firm opposition to plans by Mr Walsh and two senior colleagues - chief financial officer Mr Brian Dunne and chief operations officer Mr Seamus Kearney - to pursue a management buyout of the airline. If successful, the men behind the proposal envisage the loss of 1,300 jobs at the airline, more than halving the staff numbers from the time they took over Aer Lingus in October 2001 as business slumped in the wake of the terrorist attacks in the United States.

A special meeting will be held tonight where union delegates, representing around 1,000 members, will discuss plans for a co-ordinated campaign against privatisation of the company.

The issue will also be discussed by hundreds of members at a series of meetings at the State's three airports to be held this week. SIPTU's national industrial secretary, Mr Michael Halpenny, said it was was "not ruling anything out" in its opposition to the plans.

He said the union would tell the Government that members must be kept fully involved in any discussions over the future of the airline under the terms of the national pay deal. "We're helped turn Aer Lingus from a company that was €60 million in debt into a commercially successful airline that's due to make a substantial profit this year.

"Our workers have made a lot of sacrifices during what was a difficult and traumatic time. We want to be involved in the future of Aer Lingus as a State enterprise, and we're more than entitled to be fully involved in that process."

Mr Halpenny also said there was a major conflict of interest with the chief executive of a State firm seeking to purchase the company he was charged with developing.

While thousands of staff could benefit from an Eircom-style windfall if the airline is sold, SIPTU's general secretary, Mr Joe O'Flynn, said members would not easily be convinced.

Mr O'Flynn said it was "imperative" that the State retained a role within Aer Lingus given the strategic importance of the company.

Other unions at the airline, including IMPACT, were unavailable for comment yesterday.

There was mixed reaction from political parties to the plans. While the Progressive Democrats leader, Ms Harney, has said the plans should be considered, Labour said there was no case for privatisation.

The party's Transport spokeswoman, Ms Róisín Shorthall, said it would not be fair to allow senior executives at Aer Lingus to pursue a process of privatisation which would allow them reap substantial financial rewards.